The present invention is generally in the area of controlled release of biologically-active compounds and in particular is a system for controlled release of biologically-active substances within specifically formulated microcapsules in conjunction with a microcapsule core-degrading enzyme.
Encapsulation of biological material as a method for delivery of a biologically-active substance, both in vivo and in vitro, is well known. U.S. Pat. No. 4,352,883 to Lim entitled "Encapsulation of Biological Material" discloses encapsulation or a core material such as living cells or proteins within a membrane that is permeable to small molecules but impermeable to larger molecules. Encapsulation is carried out by suspending the core material in an aqueous medium containing a water-soluble gum that can be reversibly gelled, forming the suspension into droplets, contacting the droplets with a solution of multivalent cations to gel the droplets as discrete, shape-retaining, water insoluble temporary capsules and ionically cross-linking a surface layer of the temporary capsules to produce a semipermeable membrane around the capsules.
The system disclosed in U.S. Pat. No. 4,352,883 relates to a process for encapsulating tissue or individual cells so that they remain viable and in a protective state within a membrane which is permeable to nutrients, ions, oxygen and other materials needed to both maintain the tissue and support its normal metabolic functions, but impermeable to bacteria, lymphocytes, and large proteins of the type responsible for immunochemical reactions resulting in rejection. In the preferred embodiment of this system, the microcapsule retains its integrity following implantation.
The technology for forming a microcapsule around a labile biologically-active substance, such as many of the glycoproteins, is well known. A two-step interfacial polymerization process for encapsulating operative chemically-active substances within semipermeable membranes is disclosed in U.S. Pat. No. 4,324,683 to Lim et al entitled "Encapsulation of Labile Biological Material". The purpose of this method is to form microcapsules with a well-controlled porosity. The microcapsule serves to protect the active substances from attack by microorganisms. Accordingly, the purpose of this disclosed method is the same as in U.S. Pat. No. 4,352,883, i.e., to preserve and protect the encapsulated material and, in particular, to avoid any immunological response against the encapsulated biologically-active material.
Methods have been developed to reversibly encapsulate biologically-active substances. For example, as disclosed by Lim in U.S. Pat. No. 4,407,957, a biologically-active material may be encapsulated and subsequently released by selective disruption of the membranes in the microcapsules. As disclosed, the encapsulation technique involves the formation of a semipermeable membrane around a droplet through the formation of multiple ionic bonds between a polyionic polymer in the droplet and a cross-linking polyionic polymer which possesses multiple ionic groups of opposite charge. The membrane can be selectively disrupted by exposing it first to a solution of competing cross-linking multivalent ions followed by a solution of a competing polyionic polymer of the same charge as the polymer in the original droplet. Alternatively, a mixed solution of the two competing solutions may be used together. Unfortunately, such a process of reversal is limited to in vitro use, for example, for the encapsulation and subsequent release of cell cultures without damage to the cells.
Another method for encapsulating biologically-active substances for subsequent release which is useful both in vivo and in vitro is described in U.S. patent applications Ser. No. 07/161,198, now U.S. Pat. No. 4,900,556, which is a continuation of U.S. Ser. No. 727,802 entitled "System for Delayed and Pulsed Release of Biologically-Active Substances" (now abandoned) and Ser. No. 07/092,554 allowed, which is a continuation of U.S. Ser. No. 727,803 entitled "System and Apparatus for Delayed and Pulsed Release of Biologically-Active Substances"(now abandoned), both filed Apr. 26, 1985 by Margaret A. Wheatley, Robert S. Langer and Herman N. Eisen. A system for controlled release of entrapped biologically-active substances, either at a constant rate over a period of time or in discrete pulses, is disclosed. The biologically-active substances are entrapped within liposomes, which are protected from the biological environment by encapsulation within semipermeable microcapsules or a permeable polymeric matrix. Release of the entrapped substance into the surrounding environment is governed by the permeability of both the liposome and the surrounding matrix to the substance. Permeability of the liposome is engineered by modifying the composition and method for making the liposomes to produce liposomes which are sensitive to a specific stimuli, such as temperature, pH or light; by including a phospholipase within some or all of the liposomes or the surrounding matrix which degrade the liposomes; by destabilizing the liposome to break down over a period of time; or by any combination of these methods. While this method is useful both in vitro and in vivo for a controlled rate of release, the system and apparatus require expertise in the processing and handling of both liposomes and microcapsules, as well as the delicate interrelationship between the two, to achieve the desired result.
It is therefore an object of the present invention to provide a method for controlled release which is useful both in vitro and in vivo.
It is a further object of the present invention to provide a method for controlled release which is simple, reliable, and versatile.
It is a further object of the invention to provide a system for controlled release which can be used for single, delayed, or multiple release of the substances over time.
It is another object of the invention to provide a system for controlled release of biologically-active substances including labile proteins as well as more stable organic and inorganic molecules.